diff --git a/B09_Estimation/B09_Estimation_UnitPrice.py b/B09_Estimation/B09_Estimation_UnitPrice.py
index b776bf41..4d5570d3 100644
--- a/B09_Estimation/B09_Estimation_UnitPrice.py
+++ b/B09_Estimation/B09_Estimation_UnitPrice.py
@@ -65,6 +65,7 @@ from B09_Estimation.B09_Estimation_ResourceAxis import (
     load_labor_catalog,
     load_work_item_master,
 )
+from B09_Estimation.B09_Estimation_WorkItemUnit import BORROWED_BASIS_PER
 from B09_Estimation.B09_Estimation_WorkItemUnit import unit_of as work_item_unit
 from B09_Estimation.B09_Estimation_Rounding import OutputPlace, round_at
 from B09_Estimation.B09_Estimation_Transport import parse_distance_km
@@ -889,9 +890,12 @@ def build_unit_prices(
             continue
 
         # ⚠ 밑수를 못 찾은 표를 쓰면 **곱하면 안 되는 줄**로 표시한다.
+        #   예외 = 사용자가 다른 품셈 밑수를 확정한 자리(9-21 「1,000㎡당」 · ÷ 는 ChooseOne 이 검) —
+        #   마스터 목록은 원문 사실이라 그대로 두고 여기서만 걷음(2026-09-14 브레인 · 사유는 비고).
+        borrowed = work_item_code.startswith(tuple(BORROWED_BASIS_PER))
         for row in rows:
             section = missing_basis.get(str(row.pum_table_id))
-            if section:
+            if section and not borrowed:
                 build.basis_missing[work_item_code] = section
                 break
 
diff --git a/resources/tester/test_b09_table_reading_2.py b/resources/tester/test_b09_table_reading_2.py
index dcaf749b..a8dd2e5f 100644
--- a/resources/tester/test_b09_table_reading_2.py
+++ b/resources/tester/test_b09_table_reading_2.py
@@ -68,3 +68,27 @@ def test_토사면_고르기는_두_표가_섞여_값이_불완전하다고_먼
     note = known_gap_note("FP-09-19-01")
     assert "절토면" in note and "성토면" in note and "불완전" in note
     assert "불완전" in detail_of(cached_build(), "B-FP-09-19-01")["known_gap_note"]
+
+
+def test_제근은_빌린_밑수가_확정이라_갈래가_서면_내역_금액이_섬() -> None:
+    """9-21 원문엔 밑수가 없어 마스터 `basis_missing` 에 F0294 가 남음(원문 사실 그대로) — 그러나
+    사용자 확정(건설품셈 3-9-2 「1,000㎡당」 · ÷1,000 은 ChooseOne 이 검)이 있어 내역에서
+    「밑수 미확보」로 막히면 안 됨(2026-09-14 브레인). 교차 참조 사유는 비고에 그대로 남음."""
+    from B09_Estimation.B09_Estimation_BasisSheet import open_gaps
+    from B09_Estimation.B09_Estimation_BillOfQuantities import build_bill
+    from B09_Estimation.B09_Estimation_UnitPrice import detail_of, load_basis_missing
+
+    assert "F0294" in load_basis_missing()
+    build = cached_build()
+    assert "FP-09-21" not in build.basis_missing
+    assert not [g for g in open_gaps(build) if g["code"] == "FP-09-21"]
+    title = "B-FP-09-21#굴착기(무한궤도)0.7·소"
+    # ㎡당 환산이 걸린 값 — 1,000㎡당 그대로면 5만원대로 섬
+    assert build.book.title(title) and 50 <= int(detail_of(build, title)["total"]) <= 60
+    item = {"work_item_code": "FP-09-21", "name": "지장목제거", "spec": "뿌리뽑기", "unit": "㎡",
+            "quantity": "1000", "in_bill": True, "variant_axis": "stand_volume_class",
+            "variant_value": "굴착기(무한궤도)0.7·소"}  # fmt: skip
+    result = build_bill({"work_items": [item], "materials": []}, build=build)
+    assert not result.missing, result.missing
+    row = next(r for r in result.rows if r.code == "FP-09-21")
+    assert row.amount_krw and int(row.amount_krw) > 0, row.note